Why the first 3 rounds of the NFL draft are critical for teams

On April 28, 2016, the NFL will hold its annual draft. NFL teams spend millions of dollars on scouting departments

so they can research, travel to workouts, interview and investigate draft picks they will spend millions of dollars on in salary. Teams are also investing for a shot to build a team based upon their philosophy and compete for a Super Bowl title.

My research found some great data at the Denver Broncos SB Nation team website regarding this topic. The article is from 2014, but still holds important numbers on the study of draft picks. Here is the methodology from the author and what was found in a graph below:

To do this I decided to go back over a decade and looked at each and every draft pick and tracked whether they were with their team each year for up to five years. I took all this data and created a complete table where I was able to see what percentage of players were on the teams that drafted them at the start of their 1st, 2nd, 3rd, 4th and 5th years.

From the same article, an excellent table showing the life of a draft pick in a five year period.
Seeing how the life span of an NFL player is short, having 2-3 good drafts in rounds one through three are very critical for teams to establish a contender.